Dispersion and slope compensating optical fiber and transmission link including same

ABSTRACT

A DCF adapted to compensate for dispersion and slope of a length of SMF in the C-band window that includes a core surrounded by a cladding layer of refractive index Δ c . The core includes at least three radially adjacent segments, a central core segment having a positive Δ 1 , a moat segment having a negative refractive index Δ 2 , and a ring segment having a positive refractive index Δ 3 , wherein Δ 1&gt;Δ3 &gt;Δc&gt;Δ 2 . The DCF exhibits a negative Dispersion Slope (DS), where −0.29 (ps/nm 2 ·km) at 1546 nm, a dispersion (D), where −100&lt;D&lt;−120 (ps.nm·km) at 1546 nm, and a κ value (D/DS) at 1546 nm that is preferably between 250 and 387 nm. The DCF preferably has a cutoff wavelength (λc) less than 1500 nm, attenuation at 1550 nm of less than 0.6 dB/km, and a bend loss of less than 0.01 dB/m on a 40 mm mandrel at 1550 nm. A transmission link including the combination of a SMF and a DCF having a dispersion (D), where −100&lt;D&lt;−120, is also disclosed.

[0001] This application claims the benefit of and priority to U.S.Provisional Application No. 60/304,662, filed Jul. 11, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to dispersion and slopecompensating optical fibers and transmission links for wavelengthdivision multiplexing (WDM) systems, and more particularly to opticalfibers and transmission links including such fibers that areparticularly well suited for compensating dispersion and slope of SingleMode Fiber (SMF) operating in the C-band.

[0004] 2. Technical Background

[0005] To meet the ongoing drive for more bandwidth at lower costs,telecommunications system designers are turning to high channel countdense wavelength division multiplexing (DWDM) architectures, longerreach systems and higher transmission bit rates. This evolution makeschromatic dispersion management critical to system performance, assystem designers now desire the ability to accurately compensatedispersion across entire channel plans. Today, the only viable broadbandcommercial technology to battle dispersion has been DispersionCompensating Modules (DCMs), i.e., spools having a suitable length ofDispersion Compensating Fiber (DCF) wound thereon. As DWDM deploymentsincrease to 16, 32, 40 and more channels, broadband dispersioncompensating products are even more desirable. Many currenttelecommunications systems have SMFs that, although they are optimizedfor zero dispersion at about 1310 nm, can also be utilized effectivelyto transmit signals at wavelengths around 1550 nm. This enableserbium-doped fiber amplifiers to be employed. An example of such a SMFis SMF-28™ manufactured by Corning Incorporated. Prior Art FIG. 2illustrates the refractive index profile for such a SMF. Typically, suchfibers exhibit a dispersion of about 17 ps/(nm·km) and a dispersionslope of about 0.058 ps/(nm²·km) at 1550 nm.

[0006] With continuing interest in higher bit rate systems (>10 Gbs),long reach systems (e.g., >500 km) and optical networking, it isimperative to use DCFs in networks that carry data on SMF as well. Highbit rates, longer reaches and wider bandwidths require dispersion, butalso dispersion slope to be compensated for more exactly.

[0007] Consequently, it is desirable for the DCF to have dispersioncharacteristics such that its dispersion and dispersion slope arematched to that of the SMF transmission fiber it is required tocompensate. The ratio of dispersion to dispersion slope at a givenwavelength is referred to as “kappa (κ).” Kappa changes as a function ofwavelength for a given transmission fiber. Hence, it is equallyimportant that the kappa value of the DCF is matched to that of thetransmission fiber in the operating window.

[0008] It would be desirable to develop alternative DCFs, in particular,ones having the ability to compensate for dispersion of SMF over a widewavelength band around 1550 nm.

SUMMARY OF THE INVENTION

[0009] The present invention is a dispersion compensating optical fiberwhich comprises a core refractive index profile which is selected toresult in a fiber which exhibits negative dispersion and negativedispersion slope at 1546 nm and preferably exhibits low bend loss andlow attenuation. The DCF in accordance with the present invention isparticularly effective at compensating for both the dispersion and slopeof a SMF in a transmission link operating within the C-band operatingwindow. More particularly, the present invention is a DCF comprising acore refractive index profile with a central core segment having apositive relative refractive index Δ1, a moat segment surrounding thecentral core segment having negative relative refractive index Δ2, and aring segment which surrounds the moat segment having a positive relativerefractive index Δ3, wherein Δ1>Δ3>Δ2,

[0010] And where Δ is defined as:$\Delta = {\frac{\left( {n_{1}^{2} - n_{c}^{2}} \right)}{2n_{1}^{2}} \times 100.}$

[0011] The DCF in accordance with a first embodiment of the inventionexhibits a core refractive index profile that results in a negativedispersion slope of less than −0.29 ps/(nm²·km) at a wavelength of 1546nm, a negative dispersion of between −100 ps/(nm·km) and −120 ps/(nm·km)at a wavelength of 1546 nm, and a kappa value obtained by dividing thedispersion by the dispersion slope at 1546 nm in the range between of250 to 387 nm. The DCF preferably has a cladding layer surrounding thering segment and having a relative refractive index Δc, whereinΔ1>Δ3>Δc>Δ2.

[0012] The DCF in accordance with another embodiment of the inventionexhibits a core refractive index profile that results in a negativedispersion slope of less than −0.29 ps/(nm²·km) and greater than −0.40ps/(nm²·km) at a wavelength of 1546 nm, and more preferably less than−0.36 and greater than −0.40 ps/(nm²·km) at 1546 nm. In accordance withthe invention, the DCF also exhibits a negative dispersion of between−100 ps/(nm·km) and −120 ps/(nm·km) at a wavelength of 1546 nm, and morepreferably between −105 ps/(nm·km) and −120 ps/(nm·km) at 1546 nm. TheDCF in accordance with the invention preferably exhibits a kappa valueobtained by dividing the dispersion by the dispersion slope at 1546 nmin the range between of 250 to 387 nm. The DCF preferably has a claddinglayer surrounding the ring segment and having a relative refractiveindex Δc, wherein Δ1>Δ3>Δc>Δ2.

[0013] Advantageously, the cutoff wavelength (λ_(c)) of the DCF is lessthan 1500 nm and more preferably less than 1350 nm. Low cutoffwavelength in a DCF is advantageous because it provides a system thatmay only propagate light in the fundamental mode. Thus, Multiple PathInterference (MPI) may be significantly reduces which, therefore,reduces system noise in the C-band wavelength window.

[0014] In accordance with another embodiment of the DCF of the presentinvention, the peak delta Δ1 of the central core segment is greater than1.6% and less than 2.0%, and more preferably greater than 1.7% and lessthan 1.9%. The lowest delta Δ2 of the moat segment is less than −0.25%and greater than −0.44%, and is more preferably less than −0.30% andgreater than −0.37%. The peak delta Δ3 of the ring segment is greaterthan 0.2% and less than 0.5%, and more preferably greater than 0.35% andless than 0.45%.

[0015] In accordance with another embodiment of the invention, thedispersion compensating optical fiber has an outer radius r₁ of thecentral core segment between 1.5 and 2 microns; an outer radius r₂ ofthe moat segment between 4 and 5 microns; and a center radius r₃ of thering segment between 5.5 and 7 microns. More preferably, the outerradius r₁ of the central core segment is between 1.6 and 1.8 microns;the outer radius r₂ of the moat segment is between 4.2 and 4.8 microns;and the center radius r₃ of the ring segment is between 6 and 6.5microns.

[0016] According to another embodiment of the invention, the dispersioncompensating optical fiber has a core/moat ratio, taken as r1/r2, thatis greater than 0.34 and less than 0.40 and an effective area (Aeff) at1546 nm that is greater than 18 square microns, and more preferablygreater than 20 square microns. This large effective area is desirableas it can reduce non-linear effects. The DCF preferably exhibits anattenuation of less than 0.6 dB/km at 1550 nm thereby not appreciablyadding to the total attenuation of the transmission link. Additionally,the DCF preferably exhibits a bend loss that is less than 0.01 dB/m, andmore preferably less than 0.005 dB/m at 1550 nm on a 40 mm diametermandrel. Low bend loss is very important in DCF's as it allows forcompact packaging on the modules and helps to keep the total linkattenuation low.

[0017] In accordance with a preferred embodiment of the invention, theDCF includes a ring segment having a lower delta tail portion that meetsthe zero delta % at a radius greater than 8 microns, more preferablygreater than 10 microns, and most preferably greater than 12 microns.The tail portion 40 preferably has a delta % of greater than 0.02% andless than 0.2% at a radius between 7 and 8 microns. Preferably, the tailportion tapers linearly from about 8 microns to the zero delta % 42.

[0018] In another embodiment of the invention, an optical fibertransmission link is provided comprising a length of SMF optimized forlow dispersion operation at a wavelength range of 1290 nm to 1320 nm;and a length of DCF having a dispersion value between −100 and −120 at1546 nm wherein within a transmission band of between 1520 nm to 1570 nmthe transmission link exhibits an absolute value of residual dispersionless than about 0.15 ps/km/nm. Preferably, the length of SMF is greaterthan 6 times, and more preferably greater than 7 times, the length ofthe length of DCF.

[0019] Additional features and advantages of the invention will be setforth in the detailed description which follows, and will be readilyapparent to those skilled in the art from that description or recognizedby practicing the invention as described herein, including the detaileddescription which follows, the claims, as well as the appended drawings.

[0020] It is to be understood that both the foregoing generaldescription and the following detailed description are merely exemplaryof the invention, and are intended to provide an overview or frameworkfor understanding the nature and character of the invention as it isclaimed. The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate various embodimentsof the invention, and together with the description serve to explain theprinciples and operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIGS. 1 illustrates a transmission link including the DCF inaccordance with the invention.

[0022]FIG. 2 illustrates a refractive index profile of a SMF inaccordance with the Prior Art.

[0023]FIG. 3 illustrates a sectioned perspective view of the DCF inaccordance with the invention.

[0024]FIG. 4 illustrates a refractive index profile of a DCF inaccordance with the present invention.

[0025]FIG. 5 is a plot illustrating residual dispersion in atransmission link including the combination of DCF and SMF in accordancewith the present invention.

[0026]FIG. 6 illustrates a refractive index profile of anotherembodiment of DCF in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0027] Reference will now be made in detail to the present preferredembodiments of the invention, an example of which is illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.Drawings should not be construed to be to scale. An exemplary embodimentof a transmission link including the DCF in accordance with the presentinvention is shown in FIG. 1.

[0028] The transmission link 20 includes a length of SMF 22 having apositive dispersion of about 17 ps/(nm·km) at 1550 nm and positivedispersion slope of about 0.058 ps/(nm²·km) at 1550 nm. The link 20 alsoincludes a length of DCF 24 in accordance with the invention which is adispersion and dispersion slope compensating optical fiber having ageometry and core refractive index profile as shown in FIGS. 3 and 4,respectively. The DCF has a central cylindrical core segment 30 having apositive relative refractive index Δ1, an annular moat segment 32surrounding and abutting the central core segment 30 that has a negativerelative refractive index Δ2, and an annular ring segment 34 abuttingand surrounding the moat segment 32 having a positive relativerefractive index Δ3. In particular, the shape of the refractive indexprofile is such that Δ1>Δ3>Δ2 as best shown in FIG. 4.

[0029] The DCF in accordance with the present invention, has a corerefractive index profile that results in a fiber exhibiting a negativedispersion slope of less than −0.29 ps/(nm²·km) at a wavelength of 1546nm, and a negative dispersion of between −100 ps/(nm·km) and −120ps/(nm·km) at a wavelength of 1546 nm. More preferably, the dispersionslope at 1546 nm is less than −0.29 ps/(nm²km) and greater than −0.40ps/(nm²·km), and more preferably yet less than −0.36 ps/(nm²·km) andgreater than −0.40 ps/(nm²·km) at a wavelength of 1546 nm. Mostpreferably, the dispersion at 1546 nm is between −105 and −120ps/(nm·km). This DCF's attributes are ideal for compensating dispersionand dispersion slope within a transmission link including a length ofSMF operating in the C-band (1520 nm to 1570 nm). Most preferably, theDCF exhibits a kappa value (κ) obtained by dividing the Dispersion (D)by the dispersion slope (DS), i.e., D/DS, at 1546 nm of between 250 and387 nm. As can be seen in FIG. 3, the fiber also preferably includes anannular cladding layer 36 having a relative refractive index Δc thatsurrounds and abuts the ring segment 34. In particular, the refractiveindex profile of the fiber 24 is such that Δ1>Δ3>Δc>Δ2.

[0030] Again referring to FIG. 4, the refractive index profile 29 of theDCF 24 has an up-doped central core segment 30 having peak Δ1. The coresegment 30 is surrounded by a down-doped moat segment 32 having peaknegative Δ2, which is in turn surrounded by an up-doped annular ringsegment 34 having peak Δ3. All of the aforementioned are surrounded bythe preferably pure silica cladding layer 36 and a protective polymercoating 38, such as a urethane acrylate. The coating 38 preferablyincludes a primary and secondary coating portions of lower and highermodulus, respectively, as is conventional. Preferably, segments 30 and34 are formed using suitable amounts of germania-doped SiO₂, althoughother forms of index refraction increasing dopants could also beemployed to achieve the fibers disclosed herein, so long as the samegeneral refractive index profile is achieved. Likewise, whereas segment32 is preferably formed using fluorine-doped SiO₂, other index ofrefraction decreasing dopants could be employed besides fluorine. Asmentioned above, the cladding layer 36 is preferably formed of puresilica. However, the cladding region 36 may also include index ofrefraction increasing or decreasing in dopants, so long as the relativeΔ versus radius relationship illustrated in FIG. 4 is maintained.

[0031] In one embodiment of the DCF illustrated in FIG. 4, Δ1 is greaterthan 1.6% and less than 2.0% and comprises an outer radius r₁ (in FIG.1, r₁ is drawn to the point where the profile intersects the zero deltax-axis) between 1.5 and 2 microns. Δ2 is less than −0.25% and greaterthan −0.44%, and has an outer radius r₂ which ranges between 4 and 5microns. According to the invention, Δ3 is greater than 0.3% and lessthan 0.5% and comprises a center radius r₃ (as measured from a centerpoint of a line dissecting the half height points of the segment) ofbetween 5.5 to 7 microns. Radius, as used herein, means the distancemeasured from the centerline of the optical fiber to the outer point ofthe segment, i.e., where the outermost region of the index segmentintersects the x-axis (which is also equal to the index of the claddinglayer 38). Center radius, on the other hand, is measured to the centerof the core segment as determined by the half height points.

[0032] More preferably, Δ1 of segment 30 is between 1.7 and 1.9% andcomprises an outer radius r₁ between 1.6 to 1.8 microns, Δ2 of moatsegment 32 is between −0.3% and −0.37%, and has an outer radius r₂between about 4.2 and 4.8 microns. The annular ring segment 34preferably exhibits a Δ3 greater than 0.3% and less than 0.45% and acenter radius of 5.2 to 5.8 microns, and a half-height width betweenabout 0.5 to 1.5 microns, and most preferably about 1 micron.

[0033] In a preferred embodiment, Δ1 of the core segment 30 is greaterthan 1.6% and less than 2.0% and comprises an outer radius between about1.5 to 2 microns, Δ2 of the moat segment 32 is less than −0.25% andgreater than −0.44%, and has outer radius r₂ between 4 and 5 microns,and Δ3 of ring segment 34 is greater than 0.2% and less than 0.5% andcomprises a center radius r₃ between 5.5 to 7 microns.

[0034] In a preferred embodiment, the DCF includes a ring segment 34having a lower delta tail portion 40 that meets the zero delta % 42 at aradius greater than 8 microns, more preferably greater than 10 microns,and most preferably greater than 12 microns. The tail portion 40preferably has a delta % of greater than 0.02% and less than 0.2% at aradius between 7 and 8 microns. Preferably, the tail portion tapersapproximately linearly from about 8 microns to the zero delta % 42. Thetail portion 40 improves the bend loss of the DCF.

[0035] DCFs made in accordance with the invention preferably exhibit afiber cut off wavelength (λc) which is less than the C band (i.e. lessthan 1500 nm, and more preferably less than 1350 nm). Consequently, whenclad with silica cladding, the fibers disclosed herein are desirablysingle moded at 1550 nm.

[0036] It should be noted that the fibers disclosed in here do notnecessarily have to be employed only in dispersion compensating modules,and instead the fibers could be employed in dispersion compensatingfiber cables (rather than enclosed modules that are typically employedin boxes).

[0037] In a preferred embodiment, the dispersion compensating opticalfibers disclosed herein are deployed in such dispersion compensatingmodules wherein the fiber is wound around a hub. Preferably the hub iscylindrical, and has a diameter of less than about 12 inches, morepreferably less than about 10 inches, and most preferably less thanabout 6 inches, and the length of fiber deployed therein is typicallygreater than 1 km. In accordance with an embodiment of the invention,when used in a transmission link, the ratio of the length of the SMF tothe length of DCF is preferably greater than 6:1, more preferablygreater than 7:1 and in the system shown in FIG. 1, was about 7.14:1.

EXAMPLES

[0038] The invention will be further illustrated by the followingexamples which are meant to be illustrative and an exemplary of theinvention.

[0039] In Example 1, a fiber having the refractive index profileillustrated in FIG. 4 was made having a central core segment 30 withpeak Δ1=1.84% and an outer radius r₁ of 1.57 microns, a lowest Δ2 in themoat segment 32 of about −0.33% and an outer radius r2 of 4.55 microns,and a ring segment peak Δ3 equal to about 0.4% with a ring center radiusr3 of about 6.25 microns and a half height width of about 1 micron. Theraised index regions 30 and 34 were formed using germania doping, andthe lowered index region 32 was formed using fluorine doping. Outer cladregion 36 is pure silica, and the outer diameter of the resultant fiberwas 125 microns. The resultant fiber exhibited dispersion at 1546 nm ofapproximately −110 ps/nm-km, a dispersion slope of about −0.39 and a κvalue of about 282 nm. The effective area of this fiber wasapproximately 20.2 square microns at 1546 nm, and the fiber cutoffwavelength was 1340 nm. Bend loss was 0.0035 dB/m on a 40 mm mandrel at1550 nm and attenuation is less than 0.5 dB/km at 1550 nm.

[0040] Additional examples of embodiments in accordance with theinvention are listed in Table 1. The corresponding Δ versus radiusrelationships of each of these examples is set forth in Table 1 below,wherein the radii of the Δ1 and Δ2 segments are outer radii, and theradius of Δ3 is a center radius. Also set forth for Δ3 is the halfheight width. All of the radius and half-height width values are setforth in microns. Also set forth are the corresponding dispersionproperties, including dispersion measured at 1546 nm, dispersion slopeat 1546 nm, kappa κ at 1546 nm, and the fiber cut off wavelength (λc).TABLE 1 Outer Outer Ctr. r₁ r₂ r₃ Fiber Δ1 (μm) Δ2 (μm) Δ3 (μm) D₁₅₄₆D_(slope) κ cutoff Ex. 1.84 1.57 −.33 4.55 .40 6.25 −110 −0.39 282 13401 Ex. 1.83 1.68 −.37 4.64 .43 6.42 −101 −0.31 326 1496 2 Ex. 1.85 1.64−.37 4.45 .41 6.12 −120 −0.34 353 1445 3

[0041] As the role of waveguide dispersion is made larger in order toattain DCF's with ultra high negative dispersion slopes, the DCFs becomemore bend sensitive. One way to reduce the bend sensitivity of the fiberis to reduce the effective area of the fiber. This however can havenegative impact on the system performance via increased non-lineareffects. Hence, proper design of a DCF with high negative dispersionslope for broadband WDM systems requires a careful optimization of thebend sensitivity of the fiber while keeping the effective area of thefiber as large as possible.

[0042] The present invention has an effective area (Aeff) greater than18 μm², and more preferably greater than 20 μm² and attenuation that isless than 0.6 dB/km. All of the results shown in Table 1 above are forfibers that were drawn to 125 micron diameter fiber.

[0043] Another embodiment of DC fiber in accordance with the inventionis shown in FIG. 6 herein. The DCF in accordance with the presentinvention, has a core refractive index profile that results in a fiberexhibiting a negative dispersion slope of less than −0.29 ps/(nm²·km) ata wavelength of 1546 nm, and a negative dispersion of between −100ps/(nm·km) and −120 ps/(nm·km) at a wavelength of 1546 nm, and a kappavalue (κ) obtained by dividing the Dispersion (D) by the dispersionslope (DS), i.e., D/DS, at 1546 nm of between 250 and 387 nm. Mostpreferably, the dispersion at 1546 nm is between −105 and −120ps/(nm·km). The DCF preferably exhibits a structure the same as shown inFIG. 3. In particular, the refractive index profile of the fiber 24 issuch that Δ1>Δ3>Δc>Δ2. Table 2 below described the attributes andstructure for the embodiment of FIG. 6 designated as Ex. 4.

[0044] The refractive index profile 29 of the DCF 24 has an up-dopedcentral core segment 30 having peak Δ1, a down-doped moat segment 32having peak negative Δ2, and an annular ring segment 34 having peak Δ3.The fiber 24 includes a pure silica cladding layer 36 and a conventionalprotective polymer coating 38. In the embodiment of the DCF illustratedin FIG. 6, Δ1 is greater than 1.6% and less than 2.0% and comprises anouter radius r₁ (in FIG. 6, r₁ is drawn to the point where the profileintersects the zero delta x-axis) of between 1.5 and 2 microns. Δ2 isless than −0.25% and greater than −0.44%, and has an outer radius r₂which ranges between 4 and 5 microns. According to the invention, Δ3 isgreater than 0.3% and less than 0.5% and comprises a center radius r₃(as measured from a center point of a line dissecting the half heightpoints of the segment) of between 5.5 to 7.5 microns. Radius, as usedherein, means the distance measured from the fiber centerline to theouter point of the segment, i.e., where the outermost region of theindex segment intersects the x-axis (which is also equal to the index ofthe cladding layer 36). Center radius, on the other hand, is measured tothe center of the core segment as determined by the half height points.

[0045] In the embodiment of FIG. 6, the DCF includes a ring segment 34having a lower delta tail portion 40 that meets the zero delta % 42 at aradius greater than 8 microns, more preferably greater than 10 microns.The tail portion 40 preferably has a delta % of greater than 0.02% andless than 0.2% at a radius of 8 microns. Preferably, the tail portiontapers approximately linearly from about 8 microns to the zero delta %42.

[0046] DCFs made in accordance with the invention preferably exhibit afiber cut off wavelength (λc) which is less than the C band (i.e. lessthan 1500 nm, and more preferably less than 1350 nm). Consequently, whenclad with silica cladding, the fibers disclosed herein are desirablysingle moded at 1550 nm. TABLE 2 Outer Outer Ctr. r₁ r₂ r₃ Fiber Δ1 (μm)Δ2 (μm) Δ3 (μm) D₁₅₄₆ D_(slope) κ cutoff Ex. 1.84 1.69 −.33 4.61 .406.67 −114 −0.41 278 1460 4

[0047] The fibers described in accordance with the invention herein haveexcellent utility as DCFs for operation in the C-band to compensate forthe dispersion and slope created in optical communications systems whichemploy SMF fiber optimized for zero dispersion at about 1310 nm, forexample SMF-28™ manufactured by Corning Incorporated.

[0048] Consequently, in the embodiment of FIG. 1 that is optimized toenable broadband dispersion compensation for SMF across the C-band, aDCF such as Example 1 may be employed to compensate for dispersionacross the C-band. Such optical communications links 20, typicallyconsists of, for example, at least a signal component 26, such as atransmitter or amplifier and second component 28, such as a signalreceiver or amplifier, and one or more amplifiers or band pass filtersthat optically interconnect the SMF and DCF (shown collectively as block27) over the path of communication.

[0049]FIG. 5 illustrates the residual dispersion as a function ofwavelength while using the DCF of example 1 in the C-band. As can beseen the absolute value of residual dispersion across the C-band is lessthan 0.15 ps/(nm·km). Thus for the example shown, 100 km of SMF arelinked to about 14.27 km of DCF in accordance with the invention. Thisresults in less than 15 ps/nm dispersion at the band edges 44 a, 44 b,as shown in FIG. 5. The plot illustrates that the DCF in accordance withthe invention compensates for the dispersion of the SMF at nearly 99%over the entire C-band window. The relative parallelism of the two lines(the SMF 46 and the DCF 48) illustrate that the slope of the SMF is alsovery well compensated for.

[0050] The DCF in accordance with the invention is preferablymanufactured utilizing standard OVD methods. The core segment 30 isformed by depositing germania-doped silica soot onto a rotating aluminamandrel. The mandrel is then removed and the soot preform isconsolidated into transparent consolidated preform. The consolidatedpreform is then drawn in a draw furnace into core cane (slender rod)while simultaneously closing the centerline aperture under a vacuum. Asegment of the core cane is placed back into a lathe and further silicasoot is deposited thereon by an OVD method. The soot laden core cane isdoped with fluorine in a consolidation furnace introducing CF₄ therein.Subsequently the fluorinated soot preform is fully consolidated therebyforming the fluorine doped region corresponding to moat segment 32. Theconsolidated blank is again redrawn into a core cane and additionalgermania-doped soot is applied by OVD thereon to form the regioncorresponding to the ring segment 34. The soot laden cane is againconsolidated an redrawn into a core cane as before mentioned. It shouldbe recognized that this core cane now includes regions corresponding tothe core, moat and ring segments. Finally silica soot is applied ontothe core cane by an OVD method and the soot laden cane is againconsolidated. This forms the final consolidated preform from which fiberwill be drawn. The preform is then transferred to a draw furnace wherefiber is drawn therefrom using conventional techniques.

[0051] It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit and scope of the invention. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1-38. (canceled).
 39. An optical fiber transmission link, comprising: a length of SMF optimized for low dispersion operation at a wavelength range of between 1300 nm to 1320 nm; and a length of DCF having a dispersion value between −100 ps/(nm·km) and −120 ps/(nm·km) at 1546 nm; wherein within a transmission band of between 1520 nm to 1570 nm the link exhibits an absolute value of residual dispersion less than 0.15 ps/km/nm.
 40. The transmission link of claim 39 wherein the length of SMF is greater than 6 times the length of the length of DCF.
 41. The transmission link of claim 40 wherein the length of SMF is greater than 7 times the length of the length of DCF.
 42. The transmission link of claim 39 wherein the DCF further comprises a dispersion slope of less than −0.29 ps/(nm²·km) and greater than −0.40 ps/(nm²·km) at a wavelength of 1546 nm.
 43. The transmission link of claim 39 wherein the DCF comprises a kappa value obtained by dividing the dispersion by the dispersion slope at 1546 nm of between 250 and 387 nm.
 44. The transmission link of claim 39 wherein the DCF exhibits a cutoff wavelength (λ_(c)) is less than 1500 nm.
 45. The transmission link of claim 39 wherein the DCF further comprises an outer radius r₁ of a central core segment between 1.5 and 2 microns; an outer radius r₂ of a moat segment is between 4 and 5 microns; and a center radius r₃ of a ring segment is between 5.5 and 7 microns.
 46. The transmission link of claim 45 wherein the DCF further comprises: a Δ1 that is greater than 1.6% and less than 2%, a Δ2 that is less than −0.25% and greater than −0.44%, and a Δ3 that is greater than 0.2% and less than 0.5%.
 47. The transmission link of claim 39 wherein the DCF has an effective area (Aeff) at 1546 nm greater than 18 square microns.
 48. The transmission link of claim 39 wherein the DCF has a bend loss less than 0.01 dB/m on a 40 mm mandrel at 1550 nm.
 49. The transmission link of claim 39 wherein the DCF has an attenuation less than 0.6 dB/km at 1550 nm. 50-61 (canceled). 